Hitherto the steel having Material No. 1.4876 in the Steel List of the Verein deutscher Eisenhuttenleute has been used for particles which must be resistant to carbonization, sulphidization and oxidation in the temperature range of 500.degree. to 1000.degree. C., more particularly with cyclic stressing. The steel consists of (in % by weight) max. 0.12% carbon, max. 1.0% silicon, max. 2.0% manganese, 19-23% chromium, 30-34% nickel, 0.15-0.60% titanium, 0.15-0.60% aluminium, residue iron. For less stringent corrosion conditions that steel is a cheap alternative to the high nickel containing materials, for example, the nickel alloy having Material No. 2.4856.
However, this austenitic steel 1.4876 shows heavy carbonization at temperatures above 900.degree. C., taking the form of a distant increase in weight due to heavy carbide precipitations and carbon absorption. As a result the mechanical properties, more particularly long-term strength, are also unfavourably affected thereby. The austenitic steel 1.4876 shows clear damage due to sulphur absorption even in oxidizing/sulphidizing conditions such as, for example, a gaseous atmosphere of nitrogen and 10% SO.sub.2 at 750.degree. C.
The austenitic steel disclosed in EP 0 135 321 containing details in % by weight) max. 0.03% carbon, 20-35% chromium 17-50% niobium and 2-6% silicon, is as a result of its high silicon content resistant to corrosion in heavily oxidizing mineral acids, such as nitric acid, but is not suitable for use at temperatures above 500.degree. C. in carbonizing, sulphidizing and oxidizing conditions.
GB PS 2 036 077 discloses an austenitic steel consisting of (details in % by weight): max. 0.10% carbon, 1-5% silicon, max. 3% manganese, 15-30% chromium, 7-45% nickel, max. 0.10% aluminium, calcium+rare earths to a maximum total of 0.10% and max. 0.03% nitrogen.
In comparison with the aforementioned steel of Material No. 1.4876, this steel shows improved resistance to oxidation with cyclic loading at temperatures up to 1100.degree. C., more particularly due to carbon contents which are lower than 0.10% by weight and also by a limitation of the sulphur content to values smaller than 0.003, preferably 0.0015% by weight. However, due to the limitation of the carbon and nitrogen contents to lower than 0.10 and 0.03% by weight respectively to obtain improved resistance to oxidation, the heat resistance of the material is inadequate in the temperature range indicated for its use. Moreover, it is technically very expensive to obtain these limitations in carbon, nitrogen and sulphur during the melting of this steel.
It is an object of the invention to provide an austenitic steel which can be used without limitation in the temperature range of 500.degree. to 1000.degree. C. in carbonizing, sulphidizing and oxidizing conditions, more particularly with cyclic stressing.